During operation of the integrated circuit including the input protection device thus constructed in the semiconductor structure, a current caused by a high voltage surge may occur at the input rod 10 of the circuit. As the current is passed through the input protection resistors 16 and 18 to the input transistor 14, the high voltage surge is on one hand attenuated by the input protection resistors 16 and 18 and is on the other hand taken up by means of the input protection transistor 20. In the semiconductor structure shown in FIGS. 2 and 3, the current flowing through the metallized input wiring layer 32 as caused by the voltage surge is applied from the input wiring layer 30 to the polysilicon resistor region 17 and may damage the polysilicon at the contact surface of the resistor region with the metallized input wiring layer 32. When this takes place, the patterned polysilicon resistor region 17 is broken and is disabled from attenuating the high voltage surge of the current flowing through the metallized layer. The present invention contemplates provision of a useful solution to such a problem inherent in an input protection device serving as a voltage surge suppressor.
It is, accordingly, a prime object of the present invention to provide a semiconductor integrated circuit having an input protection device providing reliability of operation responsive to a high voltage surge which may occur at an input to an input transistor of the circuit.